/Engine/Source/Runtime/Core/Public/Misc/Fork.h
Currently the game code is responsible for calling Fork on itself than callingFForkProcessHelper::OnForkingOccuredto transform the forkable threads. Ideally the fork point is done right after the game has loaded all the assets it wants to share so it can maximize the shared memory pool. From the fork point any memory page that gets written into by a forked process will be transferred into a unique page for this process.
class FForkProcessHelper